Method and arrangement in a telecommunication system for handling status information of data units

ABSTRACT

A method is provided in a receiving node for handling status information of data units transmitted from a sending node to the receiving node over a radio link. The receiving node establishes ( 401 ) that a number of data units that has been transmitted by the sending node are missing. The receiving node sends ( 402 ) a reduced status message to the sending node over the radio link, which message is reduced such that it comprises the negative acknowledgement for a first part of missing data units and omits negative acknowledgements for the rest of the missing data units. The omitted negative acknowledgement for the rest of the missing data units will not erroneously be interpreted as correctly received data units by the sending node.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/947,339, filed Nov. 20, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/159,711, filed Jan. 21, 2014, now U.S. Pat. No.9,197,375, which is a continuation of U.S. patent application Ser. No.12/866,534, filed Aug. 6, 2010, now U.S. Pat. No. 8,687,548, whichclaims priority from International Patent Application No.PCT/SE2008/051047, filed Sep. 18, 2008, which claims priority from U.S.Provisional Patent Application No. 61/027,110 filed Feb. 8, 2008, all ofwhich are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention basically relates to the general field of dataunit communication comprising a method and an arrangement in a sendingnode and a method and an arrangement in a receiving node. In particular,it relates to handling status information of data units transmitted fromthe sending node to the receiving node over a radio link.

BACKGROUND

In today's data unit communication, an amount of data is divided intoindividual units, and said units are transmitted to a desired receiverover an appropriate communication path. This form of data communicationis very well known and in wide use. The sending node may e.g. be a radiobase station and the receiving node may be a user equipment such as amobile phone, portable computer, Personal Digital Assistant (PDA) orvice versa. Most of these systems use bi-directional radio communicationwhere both nodes transmit and receive data units simultaneously oralternating.

Such data units carry a variety of names in the context of differentcommunication systems and communication protocols, such as packets,frames, segment, protocol data units, etc. The term “data unit” as usedin the present specification and claims generically refers to any suchdivision of a data amount.

In order to ensure the complete and correct transmission of data unitsfrom a transmitting to a receiving protocol peer, a mechanism referredto as ARQ (Automatic Repeat reQuest) is often used. ARQ mechanisms arecommonly part of link layer protocols such as the Radio Link Control(RLC) protocol or the Medium Access Control (MAC) protocol specified forthe Universal Mobile Telecommunications System (UMTS) Terrestrial RadioAccess Network (UTRAN) as well as for the Evolved-UTRAN. When using anARQ mechanism, the receiver of data units sends feedback messages to thesender, such that the sender can determine whether sent data units wereproperly received, and if not, to appropriately perform retransmissionsof data units.

A feedback message is a control data unit that is typically sent fromthe receiving entity of an ARQ protocol to the transmitting peer entity.

Feedback messages are often referred to as status message, statusreport, status, etc. They may have different formats depending on theprotocol specification. Known implementations of such status messagescomprise one or more references to protocol data units, or partsthereof, received or expected by the receiving protocol entity. Thesereferences are typically denoted as positive and/or negativeacknowledgements and also referred to as ACK or NACK. An acknowledgementprovides the transmitting protocol entity with information aboutsuccessful or unsuccessful reception of one or more data units at thereceiving protocol entity. Many of the known ARQ protocols assign aso-called sequence number (SN) to each data unit and use this sequencenumber as reference in status messages. A positive acknowledgement forthe data unit with a given sequence number may then be referred to asACK_SN whereas a negative acknowledgement may be denoted as NACK_SN.Widely, known protocols use lists and/or bitmaps in status messages. Anacknowledgement may be explicit, i.e., represent the state of oneparticular data unit or it may be cumulative, i.e., provide informationabout the state of a collection of data units.

The radio link control protocol specified for E-UTRAN uses combinationsof the two. In said protocol the positive acknowledgement is cumulative,i.e., it positively acknowledges all data units with a sequence numberup to but not including ACK_SN that are not explicitly negativelyacknowledged. In the status messages of said protocol a negativeacknowledgement is transmitted by means of a NACK_SN field for each notreceived data unit below ACK_SN.

Data units and control data units such as status messages may comprise apayload section and a header section where the former contains theactual information to be exchanged between the peer protocol entitiesand the latter carries information needed to decode that informationcorrectly. The header section of a data unit may for example comprisethe associated sequence number.

One example of a status message is the LTE RLC STATUS PDU in E-UTRANdisclosed in FIG. 1. In the example of FIG. 1, each row comprises eightbits, i.e. one octet (Oct 1, Oct 2, etc.). The data unit comprises apayload section and a header section. The header section comprises aData/Control (D/C) and a Control PDU Type (CPT) field. The D/C fieldindicates whether the data unit is an RLC data PDU carrying payload fromhigher layers or an RLC control PDU, namely a status message. The CPTfield indicates the type of the RLC control PDU. The payload sectionfollowing the header section comprises an ACK_SN field and an extensionflag E1. The former carries the sequence number following that of thehighest received data unit and it cumulatively acknowledges all dataunits up to but not including that sequence number which are notnegatively acknowledged in the remainder of the status message. The E1flag indicates whether or not a set of NACK_SN, E1 and E2 follows. TheNACK_SN field comprises the sequence number of a data unit which hasbeen detected as missing by the receiving protocol entity, i.e., anegative acknowledgement. The E2 field indicates whether or not a set ofSOstart and SOend follows. The SOstart field together with the SOendfield indicates the portion of the data unit with SN=NACK_SN (theNACK_SN which the SOstart is related to) that has been detected as lostat the receiving protocol entity. In this example the ACK_SN field aswell as all NACK_SN fields comprise 10 bit and can therefore address2¹⁰=1024 sequence numbers. In order to be able to transmit more dataunits, a wrap-around mechanism may be used so that the sequence numberspace can be re-used.

In accordance with the generic description of ARQ mechanisms thetransmitting side of an LTE RLC Acknowledged Mode (AM) RLC entityinterprets a received STATUS PDU so that all Acknowledge Mode Data (AMD)PDUs up to but excluding the AMD PDU with SN=ACK_SN have been receivedby its peer AM RLC entity, excluding those AMD PDUs indicated in theSTATUS PDU with NACK_SN and also excluding portions of AMD PDUsindicated in the STATUS PDU with NACK_SN, SOstart and SOend.

In general and also in the particular example of LTE RLC the statusmessages provide the complete status information to the ARQ sender,i.e., the status message comprises information about the entire receivewindow. Therefore, the size of the status message increases with thenumber of negative acknowledgement to be reported by the receivingprotocol entity. Due to varying radio channel quality or inappropriateresource assignments the available radio resources may not be sufficientto transmit an entire status message.

Examples of solutions to the problem that the available resources aretoo small to send a full status message are to either prioritize statusmessages to ensure that enough resources are available which impliesthat other transmissions are delayed, or to postpone the transmission ofa status message until sufficient resources are available which wouldlead to window stalling or increased transmission delays which are alsounfavourable. These solutions are likely to lead to situations where thereceiver may not be allowed to send any status message due toinsufficient radio resources.

SUMMARY

An object of the present invention is to provide a mechanism forimproving handling of a status message transmitted from a data unitreceiving node to a data unit sending node.

According to a first aspect of the present invention, the object isachieved by a method in a receiving node, for handling statusinformation of data units transmitted from a sending node to thereceiving node over a radio link. The receiving node establishes that anumber of data units being transmitted by the sending node are missing.The receiving node sends a reduced status message to the sending nodeover the radio link. The message is reduced such that it comprises thenegative acknowledgement for a first part of missing data units andomits negative acknowledgements for the rest of the missing data units.The omitted negative acknowledgement for the rest of the missing dataunits will not erroneously be interpreted as correctly received dataunits by the sending node.

According to a second aspect of the present invention, the object isachieved by a method in a sending node, for handling status informationof data transmitted from the sending node to the receiving node over aradio link. The sending node transmits a stream of data units over theradio link to the receiving node. The receiving node correctly receivessome of the transmitted data units but misses a number of thetransmitted data units. The sending node receives a reduced statusmessage from the receiving node over the radio link. The message isreduced such that it comprises the negative acknowledgement for a firstpart of missing data units and omits negative acknowledgement for therest of the missing data units. The omitted negative acknowledgement forthe rest of the missing data units will not erroneously be interpretedas correctly received data units by the sending node.

According to a third aspect of the present invention, the object isachieved by an arrangement in a receiving node for handling statusinformation of data units, transmitted from a sending node to thereceiving node over a radio link. The receiving node arrangementcomprises an establishing unit configured to establish that a number ofdata units that has been transmitted by the sending node are missing anda sending unit configured to send a reduced status message to thesending node over the radio link. The message is reduced such that itcomprises the negative acknowledgement for a first part of missing dataunits and omits negative acknowledgements for the rest of the missingdata units. The omitted negative acknowledgement for the rest of themissing data units will not erroneously be interpreted as correctlyreceived data units by the sending node.

According to a fourth aspect of the present invention, the object isachieved by an arrangement in a sending node, for handling statusinformation of data units, transmitted from the sending node to thereceiving node over a radio link. The sending node arrangement comprisesa sending unit configured to transmit a stream of data units over theradio link to the receiving node. The receiving node correctly receivessome of the transmitted data units but misses a number of thetransmitted data units. The sending node arrangement further comprises areceiving unit configured to receive a reduced status message from thereceiving node over the radio link. The message is reduced such that itcomprises the negative acknowledgement for a first part of missing dataunits and omits negative acknowledgement for the rest of the missingdata units. The omitted negative acknowledgement for the rest of themissing data units will not erroneously be interpreted as correctlyreceived data units by the sending node.

Since a reduced status report is used, comprising only the negativeacknowledgement for the first part of the sequence numbers of missingdata units but omitting negative acknowledgement for sequence numbers ofthe rest of the missed number of data units, less resources are requiredfor the transmission which in turn implies that the handling of thestatus report transmitted from the sending node to the receiving node isimproved.

Advantages of the present invention comprise that the receiving nodeinterprets the reduced status report correctly and does not advance it'stransmit window beyond any not successfully transmitted data units.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail with reference to attacheddrawings illustrating exemplary embodiments of the invention and inwhich:

FIG. 1 is a schematic block diagram illustrating a status messageaccording to prior art.

FIG. 2 is a schematic block diagram illustrating a wirelesscommunication system.

FIG. 3 is a schematic block diagram illustrating embodiments of a methodin a wireless telecommunication system.

FIG. 4 is a flow chart illustrating embodiments of a method in areceiving node.

FIG. 5 is a schematic block diagram illustrating embodiments of areceiving node arrangement.

FIG. 6 is a flow chart illustrating embodiments of a method in a sendingnode.

FIG. 7 is a schematic block diagram illustrating embodiments of asending node arrangement.

DETAILED DESCRIPTION

The invention is defined as a method and an arrangement which may be putinto practice in the embodiments described below.

FIG. 2 depicts a wireless telecommunication system 100, such as e.g.E-UTRAN, LTE, WCDMA, EDGE, and WLAN. The wireless telecommunicationsystem comprises a sending node 110 and a receiving node 120. Thesending node 110 is adapted to transmit data units such as e.g. PDUsover a radio link 130 to the receiving node 120. The sending node 110may be a base station such as a NodeB, an eNodeB or any other networkunit capable to transmit data units to a receiving node 120 over a radiolink 130. The receiving node 120 may be a wireless terminal such as amobile phone, a Personal Digital Assistant (PDA), a user equipment (UE)or any other network node capable of receiving data units from a sendingnode over a radio link 130. It may also be the opposite, so that thesending node 110 is a wireless terminal and the receiving node 120 isabuse station.

To improve throughput, the sending node 110 and the receiving node 120may use a window based Automatic Repeat request (ARQ) mechanism. In thiscase the sending node 110 comprises a transmitting window and thereceiving node 120 comprises a receiving window. The window mechanismallows the sending node 110 to continuously send data units whilewaiting for acknowledgements. The window can be seen as a buffer.

The sending node 110 may be informed about the size of the receivingwindow of the receiving node 120, to enable the sending node 110 toavoid sending more data units than the receiving node 120 canconcurrently handle. To do so, the sending node 110 may maintain a lowerwindow edge, holding the sequence number of oldest outstanding data unitfor which no positive acknowledgement has been received and an upperwindow edge holding the sequence number of the next data unit to betransmitted. It further ensures that the distance between the lower andthe upper window edge does not exceed the size of the receiver's window.With this prerequisite the sending node 110 can send a whole senderwindow of data units before receiving an acknowledgement of the firstdata unit in the window while still ensuring lossless operation andcontinuous data transmission. Upon reception of acknowledgements thelower edge of the sender window is moved forward such that the firstdata unit in the window is again the oldest transmitted but not yetacknowledged data unit.

Similarly, the receiving node 120 may maintain a lower window edgeholding the sequence number of the oldest outstanding, i.e., nextexpected data unit and an upper window edge holding the sequence numberfollowing that of the highest received data unit. Both, the lower andthe upper window edge are advanced when a data unit with thecorresponding sequence number has been received. If the lower windowedge equals the upper window edge there are no outstanding data units.Otherwise, data units may have been lost or at least re-ordered on lowerlayers and the receiving node may send a status message towards thesending node 110. Such a status message may comprise a list of sequencenumbers of expected but not yet received data units (at least the lowerwindow edge and potentially more) as well as the sequence number of thehighest received sequence number (upper window edge) or the sequencenumber following that depending on the protocol specification.

The following describes some non-limiting and non-exclusive examples howto handling status information of data units transmitted from thesending node 110 to the receiving node 120.

Referring to FIG. 3, the sending node 110 transmits data units (alsoreferred to as Protocol Data Units, PDUs or packets) to the receivingnode 120. Before the transmission, each one of the data units to betransmitted is associated with a sequence number 301 allowing thereceiving node 120 to detect re-ordering, to re-establish the data unitsoriginal order, to detect loss of data units and as a reference to beused in status messages to be sent from the receiving node 120 to thesending node 110.

The sending node 120 then transmits 302 a stream of data units over theradio link 130 to the receiving node 120. In the example of FIG. 3, dataunits with sequence numbers 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 aretransmitted to the receiving node 120. A data unit is represented by asquare containing the associated sequence number. In the example of FIG.3, data units with sequence numbers 1, 5, 9 and 10 are correctlyreceived by the receiving node 120 as indicated by straight arrows. Dataunits with sequence numbers 2, 3, 4, 6, 7 and 8 are not received or notcorrectly received by the receiving node 120 as indicated by wavyarrows.

If the channel resources allow, the receiving node 120 will send acomplete status message to the sending node 110 (not shown in FIG. 3).This complete status message may comprise a negative acknowledgement foreach one of the respective data units with sequence numbers 2, 3, 4, 6,7 and 8, i.e., it contains e.g. a NACK_SN field for each missing dataunit. The complete status message may further comprise a cumulativepositive acknowledgement for the sequence numbers 1, 5, 9 and 10, e.g.an ACK_SN field set to 11 indicating that this is the next expectedsequence number outside the receiving window.

When e.g. the channel quality is too poor for sending a complete statusmessage, as assumed in this example depicted in FIG. 3, the receivingnode 120 may send 304 a reduced status message to the sending node 110305, 306, to adapt the transmission to the available channel resourcesover the radio link 130. According to one example, the receiving node120 includes in the reduced status message, only as many negativeacknowledgements as fit in because of the limited resources whileomitting the other negative acknowledgements. In this example thereduced status message only contains three negative acknowledgements,represented e.g. by three NACK_SN fields set to the sequence numbers 2,3 and 4.

According to a state-of-the-art protocol, a cumulative positiveacknowledgement (e.g. ACK_SN) would indicate successful reception of alldata units with sequence numbers up to but excluding 11, and excludingthose data units for which an explicit negative acknowledgement iscontained. A state of the art sending node would consequently interpretthe reduced status message so as if the data units with sequence numbers6, 7 and 8 have been successfully received. It would therefore notperform retransmissions of those data units and may even discard thedata from its transmitting window so that no retransmission can beperformed later.

To overcome this problem of misunderstanding the cumulative positiveacknowledgement (e.g. ACK_SN) may be set differently for a reducedstatus message compared to a complete status message. According to afirst embodiment the positive acknowledgement (e.g. ACK_SN) in a reducedstatus message is set such that it does not acknowledge any data unitswith sequence number equal to or larger than the sequence numbers ofdata units that where omitted in the reduced status message. I.e. thereduced status message comprises positive acknowledgements only for dataunits with sequence number equal to or smaller than the lowest sequencenumbers that was omitted in the reduced status message.

In that way the sending node 110 will not erroneously interpret that thedata units missing in the receiving node's window but not reported insaid reduced status message as correctly received. In this example thismeans that the reduced status message 305 shall only positivelyacknowledge data units 1 and 5, but not data units 9 and 10. Accordingto one embodiment of this example, a method sets the ACK_SN field in thereduced status message to 6 thereby indicating to the sending node 110the successful reception of all data units up to but not includingsequence number 6 and explicitly excluding sequence numbers 2, 3 and 4.This implies that the sending node 110 receiving 306 the reduced statusmessage will treat it like any complete status message and make thecorrect status interpretation, i.e., regard the data units with sequencenumber 1 and 5 as correctly received and retransmit data units withsequence numbers 2, 3 and 4. The sending node 110 does not need to knowthat the status message is a reduced status message. It however expectsfurther status messages providing information about the otheroutstanding data units with sequence numbers 6, 7, 8 9, and 10. As abenefit of this embodiment there is no need for any indicator indicatingthat the status message is a reduced status message, i.e. that it doesnot contain negative acknowledgements (e.g. NACK_SNs) for all missing(non-received) data units or segments thereof but only for a sub-set.

In this embodiment it may be preferable not to send another statusmessage before the receiving node 120 is sure that the status messagehas been received, e.g. after receiving an expected retransmission. Toavoid sending another status message, a status prohibit timer may beapplied which may be started upon transmission of a data unit and whichprevents the receiving node from sending a status message while running.

According to a second embodiment a special identifier comprised in thestatus message used to indicate that this is a reduced status messageand not a full status message. For example, the reduced status messagemay negatively acknowledge data units (e.g. by means of one or moreNACK_SN fields) triggering retransmissions from the sending node 110 tothe receiving node 120. However, said identifier may prevent the sendingnode 110 from interpreting any not explicitly negatively acknowledgeddata units as successfully acknowledged. This means in particular thatthe sending node 110 is not allowed to advance the lower edge of itsreceiving window and from discarding any associated data units. In theexample above (not shown) a first reduced status message may containnegative acknowledgements for data units 6, 7 and 8 without beinginterpreted as a positive (cumulative) acknowledgement for the dataunits with sequence numbers 1, 3, 4, 5, 9 and 10.

A suitable field to indicate the special format may be the CPT field ine.g. the currently defined status format according to E-UTRAN. A specialcode point may be defined to indicate such special NACK message.

Several reduced status messages may be sent if the sending node 110operates according to this embodiment without causing any harm to thetransmission window state even if status messages are re-ordered orlost.

If it is known that the field of acknowledgement (e.g. ACK_SN) shouldnot be interpreted at the sending node 110, it may even be omitted, i.e.a special status message format is used for this purpose which optimizesthe size of the status message and would allow transmitting furthernegative acknowledgements in the given radio resources.

Alternatively, in this particular example the cumulative positiveacknowledgement may be set to the upper edge of the receiving window(ACK_SN=11 in this example) indicating to the sending node that at least(a segment of) the data unit with sequence number 10 has been received.

Often a status message is requested by the sending node 110 using a pollflag included in a data unit. This is typically done in order to advancethe sender window. In that case a status message according to the secondembodiment comprising only negative acknowledgement but preventing thesending node 110 from advancing its transmission window does not help.

According to a third embodiment, a special identifier comprised in thestatus message is used to indicate that this is a reduced status messageand not a full status message. Upon reception of this status message thesending node 110 may advance the lower edge of the transmission windowup to the lowest negatively acknowledged data unit. It may however notadvance it beyond the highest negatively acknowledged sequence numberunless it receives another status message allowing it to do so.

Special means such as a status prohibit timer in the receiving node 120must ensure that the receiving node 120 sends only one reduced statusmessages comprising only a sub-set of the negative acknowledgements.

In the example above (not shown in the figure) the reduced statusmessage would in addition to the special identifier contain negativeacknowledgement for the data units with sequence numbers 2, 3 and 4. Thesending node 110 can move the lower edge of the window up sequencenumber 2, i.e., remove the data unit with sequence number 1 from thetransmission window.

According to a fourth embodiment, if several reduced status messages areneeded to report all missing data units, a special status message typemay be defined for the first reduced status message comprising negativeacknowledgement closest to the lower window edge and a second specialstatus message type may be defined for the following reduced statusmessages comprising any other negative acknowledgements.

Only a reduced status message of the first special status message formatallows the sending node 110 to advance the lower window edge up to thefirst negatively acknowledged sequence number whereas the reduced statusmessage of the second special status message format must not be used toadvance the transmission window.

In this embodiment the cumulative positive acknowledgement field is notneeded and may be removed from the special status message formats inorder to save transmission resources.

In the example above (not shown in the figure) the first reduced statusmessage would comprise negative acknowledgements for the data units withsequence numbers 2, 3 and 4. A reduced status message of the secondspecial status message format comprises negative acknowledgements forthe data units with sequence numbers 6, 7 and 8.

The method steps in the receiving node 120 for handling statusinformation of data units or data unit segments “data units” transmittedfrom the sending node 110 to the receiving node 120 over a radio link130 according to some embodiments will now be described with referenceto a flowchart depicted in FIG. 4. The method comprising the steps of:

401. The receiving node 120 establishes that a number of data units 2,3, 4, 6, 7, 8 that has been transmitted by the sending node 110 aremissing.

402. The receiving node 120 sends a reduced status message to thesending node 120 over the radio link. The message is reduced such thatit comprises the negative acknowledgement for a first part 2, 3, 4 ofmissing data units and omits negative acknowledgements for the rest 6,7, 8 of the missing data units. The omitted negative acknowledgement forthe rest 6, 7, 8 of the missing data units will not erroneously beinterpreted as correctly received data units by the sending nod 110.

In some embodiments the negative acknowledgement for the first part 2,3, 4 of missing data units comprised in the reduced status message isrepresented by as many negative acknowledgements as fitted in thereduced status message because of limited resources.

The receiving node 120 may use a receiving window. In some embodimentsthe negative acknowledgement for the first part 2, 3, 4 of the missingdata units, are the missing data units which are closest to a lower edgeof the receiving window.

In some embodiments the reduced status message positively acknowledgesdata units up to but not including the first missing data unit for whicha negative acknowledgement was omitted in the reduced status message.

In one embodiment, the positively acknowledgement is performed bysetting an ACK_SN field to the first missing data unit for which anegative acknowledgement was omitted in the reduced status message,meaning that data units with sequence numbers up to but not includingthe first missing data unit for which a negative acknowledgement wasomitted, are acknowledged.

In some embodiments the reduced status message comprises an indicationthat no correctly received data units 1, 5, 9, 10 will be acknowledgedin the reduced status message such that only negative acknowledged dataunits will be triggered to be retransmitted by the sending node 110. Aspecial format of the reduced status message may be the indication thatno correctly received data units 1, 5, 9, 10 will be acknowledged in thereduced status message. In some embodiments the field of acknowledgementin the reduced status message is not used for acknowledgement, but isinstead used for a further negative acknowledgement.

403. This is an optional step. In some embodiments a first specialstatus message type is used for the reduced status message comprisingthe negative acknowledgement, for the first part 2, 3, 4 of missing dataunits closest to a lower edge of the receiving window. In this step thereceiving node 120 may send a second reduced status message to thesending node 120 over the radio link 130 using a second special statusmessage type. The second reduced status message comprises at least oneof the omitted negative acknowledgements for the rest 6, 7, 8 of themissing data units.

To perform the method steps above for handling status information ofdata units or data unit segments “data units” transmitted from thesending node 110 to the receiving node 120 over the radio link 130, thereceiving node 120 comprises an arrangement 500 depicted in FIG. 5.

The receiving node arrangement 500 comprises an establishing unit 510configured to establish that a number of data units 2, 3, 4, 6, 7, 8that has been transmitted by the sending node (110) are missing.

The receiving node arrangement 500 further comprises a sending unit 520configured to send a reduced status message to the sending node 120 overthe radio link. The message is reduced such that it comprises thenegative acknowledgement for a first part 2, 3, 4 of missing data unitsand omits negative acknowledgements for the rest 6, 7, 8 of the missingdata units. The omitted negative acknowledgement for the rest 6, 7, 8 ofthe missing data units will not erroneously be interpreted as correctlyreceived data units by the sending node 110.

The negative acknowledgement for the first part 2, 3, 4 of missing dataunits comprised in the reduced status message may be represented by asmany negative acknowledgements as fitted in the reduced status messagebecause of limited resources.

The receiving node 120 may use a receiving window and in someembodiments the negative acknowledgement for the first part 2, 3, 4 ofthe missing data units, are the missing data units which are closest toa lower edge of the receiving window.

A first special status message type may be arranged to be used for thereduced status message comprising the negative acknowledgement for thefirst part 2, 3, 4 of missing data units closest to a lower edge of thereceiving window. The sending unit 520 may further be configured to senda second reduced status message to the sending node 120 over the radiolink 130 using a second special status message type. The second reducedstatus message is arranged to comprise at least one of the omittednegative acknowledgements for the rest (6, 7, and 8) of the missing dataunits.

In some embodiments the reduced status message is arranged to positivelyacknowledge data units up to but not including the first missing dataunit for which a negative acknowledgement was omitted in the reducedstatus message.

In one embodiment the positively acknowledgement is arranged to beperformed by setting a ACK_SN field to the first missing data unit forwhich a negative acknowledgement was omitted in the reduced statusmessage, meaning that data units with sequence numbers up to but notincluding the first missing data unit for which a negativeacknowledgement was omitted, are acknowledged.

In some embodiments the reduced status message is arranged to comprisean indication that no correctly received data units 1, 5, 9, 10 will beacknowledged in the reduced status message such that only negativeacknowledged data units will be triggered to be retransmitted by thesending node 110. A special format of the reduced status message may bethe indication that no correctly received data units 1, 5, 9, 10 will beacknowledged in the reduced status message.

In some embodiments, the field of acknowledgement in the reduced statusmessage is not used for acknowledgement, but is instead arranged to beused for a further negative acknowledgement.

The method steps in the sending node 110, for handling statusinformation of data units or data unit segments “data units” transmittedfrom the sending node 110 to the receiving node 120 over the radio link130, according to some embodiments will now be described with referenceto a flowchart depicted in FIG. 6. The method comprises the steps of:

601. The sending node 110 transmits a stream of data units or data unitsegments 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, over the radio link 130 to thereceiving node 120. The receiving node 120 correctly receives some ofthe transmitted data units 1, 5, 9, 10 but misses a number of thetransmitted data units 2, 3, 4, 6, 7, 8.

602. The sending node 110 then receives a reduced status message fromthe receiving node 120 over the radio link 130. The message is reducedsuch that it comprises the negative acknowledgement for a first part 2,3, 4 of missing data units and omits negative acknowledgement for therest 6, 7, 8 of the missing data units. The omitted negativeacknowledgement for the rest 6, 7, 8 of the missing data units will noterroneously be interpreted as correctly received data units by thesending node 110.

In some embodiments, the negative acknowledgement for the first part 2,3, 4 of missing data units comprised in the reduced status message isrepresented by as many negative acknowledgements as fitted in thereduced status message because of limited resources.

In some embodiments the negative acknowledgement for the first part 2,3, 4 of missing data units are the missing data units which are closestto a lower edge of a receiving window in the receiving node 120.

In some embodiments the reduced status message positively acknowledgesdata units up to but not including the data unit for which a negativeacknowledgement was omitted in the reduced status message.

In one embodiment, the positively acknowledgement is performed bysetting an ACK_SN field to the first missing data unit for which anegative acknowledgement was omitted in the reduced status message. Thismeans that data units with sequence numbers up to but not including thefirst missing data unit, for which a negative acknowledgement wasomitted, are acknowledged.

The reduced status message may comprise an indication that no correctlyreceived data units 1, 5, 9, 10 will be acknowledged in the reducedstatus message such that only negative acknowledged data units will betriggered to be retransmitted. A special format of the reduced statusmessage may be the indication that no correctly received data units 1,5, 9, 10 will be acknowledged in the reduced status message.

In some embodiments, the field of acknowledgement in the reduced statusmessage is not used for acknowledgement, but is instead used for afurther negative acknowledgement.

603. This is an optional step. In some embodiments the sending node 110uses a transmission window. In this step the sending node 110 moves alower edge of the transmission window up to the lowest negativelyacknowledged data unit.

604. This is also an optional step. In some embodiments a first specialstatus message type is used for the reduced status message comprisingthe negative acknowledgement for the first part 2, 3, 4 of missing dataunits closest to a lower edge of the receiving window of the receivingnode 120. In this step the sending node receives a second reduced statusmessage from the receiving node 120 over the radio link 130, wherein asecond special status message type is used. The second reduced statusmessage comprises at least one of the omitted negative acknowledgementsfor the rest 6, 7, 8 of the missing data units.

In some embodiments, reception of the reduced status message of thefirst special status message type allows the sending node 110 to advancethe lower transmission window edge up to the first negativelyacknowledged sequence number whereas the reduced status message of thesecond special status message type does not allow advancing thetransmission window.

To perform the method steps above for handling status information ofdata units or data unit segments “data units” transmitted from thesending node 110 to the receiving node 120 over a radio link 130, thesending node 110 comprises an arrangement 700 depicted in FIG. 7.

The sending node arrangement 700 comprises a sending unit 710 configuredto transmit a stream of data units 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, overthe radio link 130 to the receiving node 120. The receiving node 120correctly receives some of the transmitted data units 5, 9, 10 butmisses a number of the transmitted data units 2, 3, 4, 6, 7, 8.

The sending node arrangement 700 further comprises a receiving unit 720configured to receive a reduced status message from the receiving node120 over the radio link 130. The which message is reduced such that itcomprises the negative acknowledgement for a first part 2, 3, 4 ofmissing data units and omits negative acknowledgement for the rest 6, 7,8 of the missing data units. The omitted negative acknowledgement forthe rest 6, 7, 8 of the missing data units will not erroneously beinterpreted as correctly received data units by the sending node 110.

In some embodiments the negative acknowledgement for the first part 2,3, 4 of missing data units comprised in the reduced status message isrepresented by as many negative acknowledgements as fitted in thereduced status message because of limited resources. The negativeacknowledgement for the first part 2, 3, 4 of missing data units may bethe missing data units which are closest to a lower edge of a receivingwindow in the receiving node 120. Note that sequence numbers may wraparound at some point in time so that “lower” is not relevant any longer.In this document the “lowest sequence number” refers to the sequencenumber that is closest to the lower window edge. Further, allcomparisons may be done modulo to some reference sequence number.

According to some embodiments a first special status message type isused for the reduced status message comprising the negativeacknowledgement for the first part 2, 3, 4 of missing data units closestto a lower edge of the receiving window.

The receiving unit 720 may further be configured to receive a secondreduced status message from the receiving node 120 over the radio link,wherein a second special status message type is used, and the secondreduced status message comprising at least one of the omitted negativeacknowledgements for the rest 6, 7, 8 of the missing data units.

In some embodiments the reception of the reduced status message of thefirst special status message type allows the sending node 110 to advancethe lower window edge up to the first negatively acknowledged sequencenumber whereas the reduced status message of the second special statusmessage type does not allow advancing the transmission window.

In some embodiments the reduced status message positively acknowledgesdata units up to but not including the data unit for which a negativeacknowledgement was omitted in the reduced status message.

In one embodiment the positively acknowledgement is performed by settingan ACK_SN field to the first missing data unit for which a negativeacknowledgement was omitted in the reduced status message. This meansthat data units with sequence numbers up to but not including the firstmissing data unit, for which a negative acknowledgement was omitted, areacknowledged.

The reduced status message may comprise an indication that no correctlyreceived data units 1, 5, 9, 10 will be acknowledged in the reducedstatus message such that only negative acknowledged data units will betriggered to be retransmitted.

A special format of the reduced status message may be the indicationthat no correctly received data units 1, 5, 9, 10 will be acknowledgedin the reduced status message.

In some embodiments the field of acknowledgement in the reduced statusmessage is not used for acknowledgement, but is instead used for afurther negative acknowledgement.

The sending node 110 may use a transmission window. In some embodimentsthe sending node arrangement 700 further comprises a window managingunit 730 configured to move a lower edge of the transmission window upto the lowest negatively acknowledged data unit.

The present mechanism for handling status information of data unitstransmitted from the sending node 110 to the receiving node 120 over aradio link 130, may be implemented through one or more processors, suchas a processor 530 in the sending node arrangement 500 depicted in FIG.5 or the processor 740 in the receiving node apparatus 700 depicted inFIG. 7, together with computer program code for performing the functionsof the present solution. The program code mentioned above may also beprovided as a computer program product, for instance in the form of adata carrier carrying computer program code for performing the presentsolution when being loaded into the sending node 110 or the receivingnode 120. One such carrier may be in the form of a CD ROM disc. It ishowever feasible with other data carriers such as a memory stick. Thecomputer program code can furthermore be provided as pure program codeon a server and downloaded to the sending node 110 or the receiving node120 remotely.

Some examples of the present method may be described as a method asending node 110 for handling status information of data unitstransmitted from the sending node 110 to the receiving node 120 over aradio link 130.

The method comprises the step of transmitting a stream of data units ordata unit segments over the radio link to the receiving node 120, eachdata unit being associated with a sequence number. The method comprisesthe further step of receiving a reduced status message from thereceiving node 120. The reduced status message comprises information andan indication that the reduced status massage is reduced and thereforeshall not be interpreted as a complete status message.

In some examples, the reduced status message further comprises anindication how to interpret fields in the reduced status messagecomprising the information.

The information not being complete, relates to which of the data unitsand their respective sequence number of the transmitted stream of dataunits that are received, i.e. acknowledged by the receiving node, andwhich are not received, i.e. not acknowledged by the receiving node.

Some further examples of the present method may be described as a methodin a receiving node 120 for handling status information of data unitstransmitted from a sending node 110 to the receiving node 120 over aradio link 130.

The method comprises the step of receiving a stream of data units ordata unit segments over the radio link from the sending node, each dataunit being associated with a sequence number. The method furthercomprises the step of sending a reduced status message to the sendingnode. In the reduced status message, the acknowledge of a sequencenumber associated with a data unit, e.g. the ACK_SN, is set such that itdoes not acknowledge any data units with a respective associatedsequence number equal to or larger than the not acknowledge of asequence number associated with a data unit, e.g. NACK_SNs that isomitted in the reduced status message.

When using the word “comprise” or “comprising” it shall be interpretedas non-limiting, i.e. meaning “consist at least of”.

The present invention is not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appending claims.

What is claimed is:
 1. A method in a receiving side of anAcknowledgement Mode (AM) Radio Link Control (RLC) entity for handlingstatus information of RLC Data Protocol Data Units (PDUs) transmittedfrom a peer AM RLC entity to the AM RLC entity over a radio link, eachRLC Data PDU having a respective Sequence Number (SN), the methodcomprising: determining that a number of RLC Data PDUs transmitted bythe peer AM RLC entity are missing at the AM RLC entity; generating aSTATUS PDU comprising negative acknowledgments for a first part of themissing RLC Data PDUs and omitting negative acknowledgments for the restof the missing RLC Data PDUs; setting an ACK_SN field of the STATUS PDUto the SN of the first missing RLC Data PDU for which a negativeacknowledgement is omitted from the STATUS PDU; and sending the STATUSPDU from the AM RLC entity to the peer AM RLC entity over the radiolink.
 2. The method according to claim 1, wherein the generating stepfurther comprising: including a special identifier in a Control PDU Type(CPT) field of the STATUS PDU to indicate the STATUS PDU.
 3. The methodaccording to claim 1, wherein the generating step further comprises:omitting a field of acknowledgment from the STATUS PDU to allowtransmission of additional negative acknowledgments.
 4. The methodaccording to claim 1, further comprising: generating one or more secondSTATUS PDUs comprising the rest of the missing RLC Data PDUs, whereinthe one or more second STATUS PDUs are incapable of causing the peer AMRLC entity to advance the transmission window.
 5. The method accordingto claim 1, further comprising: maintaining a lower window edgecorresponding to an SN of the oldest outstanding RLC Data PDU; andmaintaining an upper window edge corresponding to an SN of the highestreceived RLC Data PDU.
 6. A receiving side of an Acknowledgement Mode(AM) Radio Link Control (RLC) entity for handling status information ofRLC Data Protocol Data Units (PDUs) transmitted from a peer AM RLCentity to the AM RLC entity over a radio link, each RLC Data PDU havinga respective Sequence Number (SN), the AM RLC entity comprising at leastone processor; at least one memory including computer program codewhich, when executed by the processor, causes the AM RLC entity to:determine that a number of RLC Data PDUs transmitted by the peer AM RLCentity are missing at the AM RLC entity; generate a STATUS PDUcomprising negative acknowledgments for a first part of the missing RLCData PDUs and omitting negative acknowledgments for the rest of themissing RLC Data PDUs; set an ACK_SN field of the STATUS PDU to the SNof the first missing RLC Data PDU for which a negative acknowledgementis omitted from the STATUS PDU; and send the STATUS PDU from the AM RLCentity to the peer AM RLC entity over the radio link.
 7. The AM RLCentity according to claim 6, wherein the STATUS PDU further comprises aspecial identifier in a Control PDU Type (CPT) field of the STATUS PDUto indicate the STATUS PDU.
 8. The AM RLC entity according to claim 6,wherein the STATUS PDU further lacks a field of acknowledgment from theSTATUS PDU to allow transmission of additional negative acknowledgments.9. The AM RLC entity according to claim 6, wherein the memory includescomputer program code which, when executed by the processor, causes theAM RLC entity to send one or more second STATUS PDUs comprising the restof the missing RLC Data PDUs wherein the one or more second STATUS PDUsare incapable of causing the peer AM RLC entity to advance thetransmission window.
 10. The AM RLC entity according to claim 6, whereinthe memory includes computer program code which, when executed by theprocessor, causes the AM RLC entity to: maintain a lower window edgecorresponding to an SN of the oldest outstanding RLC Data PDU; andmaintain an upper window edge corresponding to an SN of the highestreceived RLC Data PDU.
 11. A method in a transmitting side of anAcknowledgement Mode (AM) Radio Link Control (RLC) entity for handlingstatus information of RLC Data Protocol Data Units (PDUs) transmittedfrom the AM RLC entity to a peer AM RLC entity over a radio link, themethod comprising: transmitting a stream of RLC Data PDUs over the radiolink to the peer AM RLC entity, the peer AM RLC entity correctlyreceiving some of the RLC Data PDUs but missing a number of RLC DataPDUs, each RLC Data PDU having a respective Sequence Number SN);receiving a STATUS PDU from the peer AM RLC entity over the radio link,wherein an ACK_SN field of the STATUS PDU is set to the SN of the firstmissing RLC Data PDU for which a negative acknowledgement is omittedfrom the STATUS PDU; and interpreting the STATUS PDU as comprisingnegative acknowledgments for a first part of the missing RLC Data PDUs,and omitted negative acknowledgments for the rest of the missing RLCData PDUs.
 12. The method according to claim 11, further comprising:receiving one or more second STATUS PDUs comprising the rest of themissing RLC Data PDUs, wherein the one or more second STATUS PDUs areincapable of causing the AM RLC entity to advance the transmissionwindow.
 13. The method according to claim 11, further comprising:maintaining a lower window edge corresponding to an SN of the oldestoutstanding RLC Data PDU for which no positive acknowledgment has beenreceived.
 14. The method according to claim 13, further comprising:advancing the lower window edge up to a next oldest outstanding RLC DataPDU in response to receiving the positive acknowledgment for the oldestoutstanding RLC Data PDU in the STATUS PDU.
 15. The method according toclaim 11, further comprising: maintaining an upper window edgecorresponding to an SN of the next RLC Data PDU to be transmitted. 16.The method according to claim 11, wherein the STATUS PDU is interpretedas the STATUS PDU with reference to a special identifier included in aControl PDU Type (CPT) field of the STATUS PDU.
 17. A transmitting sideof an Acknowledgement Mode (AM) Radio Link Control (RLC) entity forhandling status information of RLC Data Protocol Data Units (PDUs)transmitted from the AM RLC entity to the peer AM RLC entity over aradio link, the AM RLC entity comprising at least one processor; atleast one memory including computer program code which, when executed bythe processor, causes the AM RLC entity to: transmit a stream of RLCData PDUs over the radio link to the peer AM RLC entity, the peer AM RLCentity correctly receiving some of the RLC Data PDUs but missing anumber of the RLC Data PDUs, each RLC Data PDU having a respectiveSequence Number (SN); receive a STATUS PDU from the peer AM RLC entityover the radio link, wherein an ACK_SN field of the STATUS PDU is set tothe SN of the first missing RLC Data PDU for which a negativeacknowledgement is omitted from the STATUS PDU; and interpret the STATUSPDU as comprising negative acknowledgments for a first part of themissing RLC Data PDUs, and omitted negative acknowledgments for the restof the missing RLC Data PDUs.
 18. The AM RLC entity according to claim17, wherein the memory includes computer program code which, whenexecuted by the processor, causes the AM RLC entity to receive one ormore second STATUS PDUs comprising the rest of the missing RLC DataPDUs, wherein the one or more second STATUS PDUs are incapable ofcausing the AM RLC entity to advance the transmission window.
 19. The AMRLC entity according to claim 17, wherein the memory includes computerprogram code which, when executed by the processor, causes the AM RLCentity to maintain a lower window edge corresponding to an SN of theoldest outstanding RLC Data PDU for which no positive acknowledgment hasbeen received.
 20. The AM RLC entity according to claim 19, wherein thememory includes computer program code which, when executed by theprocessor, causes the AM RLC entity to advance the lower window edge upto a next oldest outstanding RLC Data PDU in response to receiving thepositive acknowledgment for the oldest outstanding RLC Data PDU in theSTATUS PDU.
 21. The AM RLC entity according to claim 17, wherein thememory includes computer program code which, when executed by theprocessor, causes the AM RLC entity to maintain an upper window edgecorresponding to an SN of the next RLC Data PDU to be transmitted. 22.The AM RLC entity according to claim 17, wherein the memory includescomputer program code which, when executed by the processor, causes theAM RLC entity to interpret the STATUS PDU as the STATUS PDU withreference to a special identifier included in a Control PDU Type (CPT)field of the STATUS PDU.